Two or more yarns are often twisted or “cabled” together to form plied yarns having various properties useful in the construction of soft floor coverings (i.e., tufted rugs and carpets). A standard cabling process involves physically rotating one yarn, fed from a creel, around a second yarn fed from a “bucket”, both yarns being under carefully controlled tension, and then winding up the combined yarns in the form of a single, twisted (piled or cabled) yarn. Once the twisted yarn is produced, it is wound onto a tube and moved over to a heat-set apparatus. Then, the twisted yarn is directed into the heat-set apparatus to form a heat-set twisted yarn.
Machines to perform this operation are sold by various manufacturers, including: Oerlikon (Volkmann), Rieter (ICBT), China Textile Machinery Corporation (CTMC), Belmont, and the like. These machines typically include a creel to hold one of the feed yarns; a tension frame to control creel yarn tension; a tube to convey the creel yarn to a spindle; a “bucket”, located above the spindle, containing the second feed yarn; tension devices; a bucket lid; and an extension arm (located no more than about 7 inches from the top of the bucket) to carry the creel yarn around the bucket yarn at specified speed (no more than 7200 rpm for over 99% of twisters currently in use and the other fraction of a percent (CTMC) claims 9000 rpm maximum).
Yarns are twisted together at frequencies ranging from about one turn to more than eight turns per inch, depending on yarn thickness and the intended effect. The higher the number of turns per inch the slower the operation becomes as the spindle carrying the creel yarn must complete a revolution for each “turn”. For example, if two yarns are twisted at about 6000 rpm, at a frequency of two turns per inch, the winding speed of the product will be approximately 3000 inches (83 yards) per minute, neglecting other factors. Doubling turn frequency to four turns per inch would approximately halve the production rate (assuming the yarns are thin enough to permit the higher level of twist). Winding speed for a commercial twisting operation is usually about 50 yards per minute up to about 100 yards per minute achieving rotational speeds of 6000 up to claims of about 9000 rpm for lighter deniers.
Other carpet related yarn processes run much more quickly than cable-twisting does today. Spinning machines wind up at speeds in excess of 3000 yards per minute, while heat setting processes wind up at about 600 yards per minute.
Thus, twisting technology is one of the limitations of the carpet industry because although twisting is important to achieve the density and resilience required of tufted carpet, cabled yarns are processed relatively slowly compared to the preceding and subsequent processes. As a result of this industry “bottleneck”, a relatively large investment in twisters and process inventory is required.
Using two distinct processes and apparatus, twisting apparatus and heat-set apparatus, is costly in terms of additional equipment, time, and square footage needed to operate.